Spark plug



' Feb. 21, 1939. R A BELL 2,147,730

SPARK PLUG Filed Dec. 24, 1937 INVENTOR Patented Feb. 21, 1939 UNITEDSTATES PATENT OFFICE Rajah Company, tion of New Jersey Bloomfield, N.J., a corpora- Application December 24, 1937, Serial No. 181,659

5 Claims.

This invention relates to spark plugs for ignition of combustible gasmixtures, e. g., in internal combustion engines.

Spark plugs as commonly made prior to the present invention commonlycomprise a core having a central electrode wire and conductor surroundedby an insulator of porcelain or other refractory insulating material anda metallic shell in which porcelain is mounted and by which the plug asa whole is handled for insertion and removal into the motor or otherlocation in which it is used. This shell also serves as the groundconnection to which the spark jumps from the center electrode wire ofthe core. According to the prior art, the bottom of the shell hasordinarily been provided with a wire or with a cage having fingersprojecting towards the center electrode, which serve respectively as asecond electrode for the spark and particularly to definitelypredetermine and locate with respect to the bottom of the spark plug theposition at which the spark occurs so as to give most efiectiveignition. It has been the practice prior to my invention to secure suchelectrode members to the lower edge of the shell by drilling a hole intowhich the electrode wire is inserted and secured or by cutting a recesstherein into which a cage electrode can be secured, e. g, by swaging.Recently, however, the tendency has been to decrease very substantiallythe dimensions permitted to spark plugs in the modern engine and thishas been carried to such an extent that the cutting required for suchmounting of the electrode may produce an objectionable weakening of theend of the plug. For this reason it has been necessary in commercialpractice to resort to spot welding of such electrodes onto the ends ofthe shell.

It is an object of my present invention to provide a plug in which theelectrode is securely mounted with a simple and efficient construction,superior in operation and length of useful service to other knownelectrode structures.

Another object of my invention is to protect the shell around theelectrode from corrosion, burning, sputtering, etc., which ordinarilyresult from severe conditions to which such plugs are subjected.

Another object of my invention is to provide a simple spark plugconstruction with an interchangeable electrode so that the heat range ofthe plug can be adjusted by use of different electrodes.

Another object of my invention is to provide a simple spark plugconstruction in which the electrodes may be replaced as simply as theplug is cleaned and thus damage which may result from burning of theelectrode may be easily repaired.

Other objects and advantages of my present 5 invention will appear fromthe following description and claims.

In the accompanying drawing and the following description I have shownand described a preferred embodiment of my invention and certainmodifications thereof. It is to be understood that these are given forpurposes of illustration in order that others may readily understand theprinciples of the invention and the manner of embodying it in practicaluse. These are not intended to be exhaustive nor limiting of theinvention but on the contrary are given for the purpose of enablingothers skilled in the 'art to modify and adapt the invention and toembody it in numerous practical forms each as may be best suited to theconditions of any particular use.

In the drawing:

Fig. 1 is a view in longitudinal section of a plug embodying myinvention;

Fig. 2 is a bottom plan View. I

Referring to the drawing, the core of the plug consists of a refractoryporcelain insulator I0, with a central electrode wire runningtherethrough. On the upper end of the electrode wire is the connectorstud 3 and near its lower end the porcelain is formed with an enlargedportion M the lower face of which is substantially conical for seatingof the soft copper gasket l5 and the upper face of which issubstantially horizontal for engagement by the centering ring IS.

The shell I1 is made in substantially the usual form with its lowerportion threaded as shown at l8 for screwing into the motor in which theplug is to be used and its upper portion 9 formed with 4 flat faces forengagement by a suitable wrench and is internally threaded forengagement of the clamping nut 9. A bore 20 extends through the smalllower end of the shell and is enlarged or recessed near its upper end,as shown at 2|, for a purpose which will be later described.

Above the recess 2| a conical seat 22 is formed for the gasket l5 whichthus serves to seal the space between the shell and the part M of thecore.

Within the bore 20 and the recess 2| is fitted a thimble shaped cageelectrode 23. This electrode, as shown, is formed of sheet metal stampedinto a thimble shape with a peripheral projection extending radiallyfrom its upper edge and fitting into the recess 2|. The sides of theelectrode thimble 23 fit closely to the inside of the bore 2!] andconstitute a lining for the shell in that part which is exposed to thehot burning gases. The end of the electrode thimble is punched out, asclearly shown in Fig. 2, to give circumferentially spaced openings 25between which are left the integral fingers 26 extending into closeproximity to the central electrode ll of the core and constituting,therefore, the electrodes proper of the shell.

As will be clearly apparent from the drawing, these electrode fingers 26are of a form such that they can be readily adjusted by bending so as togive accurately the spark gap of desired dimension but to avoidaccidental bending or substantial change in the spark gap due toheating.

The opening 25 permits the passage of gases into and out of the spacebetween the thimbleshaped electrode so as to assure the presence of anexplosive mixture surrounding the electrode when the spark occurs. Thecage form of the electrode, however, serves to hold any part of theporcelain which may be cracked or chipped off by the heat or otheraction and thus to prevent any possible scoring of the cylinder if thisshould occur. Moreover, since in the preferred embodiment of myinvention this thimble electrode is made of a metal more resistant tohigh temperature than the steel of the shell l!, e. g., of Nichrome, thelining of the shell with this material avoids the scaling anddisintegration which sometimes occurs on the inside of the shell, andespecially the sputtering of any disintegrated materials from the shellonto the porcelain where it may result in deterioration of theinsulating quality of the porcelain.

It will be observed that the assembly of this electrode thimble in theshell is accomplished simply by dropping the thimble into the bore 26 onthe inside of the shell and pushing it through the bore until itsperipheral projection 24 lies in the recess 2|. In this condition theupper edge of the electrode thimble is substantially plugged with and.forms a continuation of the gasket seat 22 and when the plug isassembled as shown in Fig. 1 the gasket 15 overlying the top of theelectrode thimble holds the latter securely in position.

It is an advantage of my invention that these electrodes are readilyinterchangeable and replaceable. If, when a plug is cleaned, it is foundthat the points are burned or otherwise damaged, the electrode thimblemay be removed and replaced by a new one and likewise if a hotter orcooler plug is required a longer or a shorter thimble may be used so asto move the position at which the spark occurs farther into the cylinderor back into the bore 20 of the plug.

What I claim is:

1. A spark plug which comprises a shell, a core extending into theshell, having a refractory insulator and an electrode wire extendingbeyond the insulator, a cage electrode surrounding the inner end of thecore and spaced from its electrode wire, said cage electrode beingthimbleshaped with a short radial projection at its periphery to engagethe shell, openings circumferentially arranged about the center adaptedfor passage of gases into and out of the space between the cage and thecore, and electrode portions extending between said openings toward theelectrode wire of the core, and said shell having a bore adapted toreceive said cage electrode from the inner end of the shell and saidbore being cut back from its inner end to form an annular seat, saidseat being recessed to receive the radial projection on the cage andthereby to position the cage at a predetermined position with respect tothe bore, a gasket engaged between the core and said seat annularlybeyond said recess, and means for pressing the core toward said seatwhereby the gasket is compressed to an air-tight seal.

2. A spark plug as defined in claim 1., in which the recess issubstantially fitted to the projection on the cage, whereby saidprojection is brought substantially flush with said seat and the gasketextends annularly over both said seat and the end and projection of saidcage whereby the cage is held by the gasket when the parts areassembled.

3. A spark plug as defined in claim 1, in which the cage electrode is asheet metal stamping of a metal more resistant to high temperatures thanthe material of the shell, and the bottom of the electrode has at leastthree circumferentially spaced holes therein and at least three integral1 fingers extending between the holes toward the electrode wire of thecore.

4. A spark plug which comprises a shell, a core extending into the shelland having an electrode and a refractory insulator therefor, and asleeve between the shell and the insulator extending at least throughoutthe space in which the burning of gases may occur and made of a materialmore refractory than the metal of said shell, whereby to preventsputtering or sublimation of the material of the shell onto theinsulator.

5. A spark plug which comprises a shell, a core extending into the shellhaving an electrode and refractory insulator therefor, and a refractorynickel-chromium alloy sleeve between the shell and the insulatorextending at least through the space in which the burning of gases mayoccur, whereby to prevent sputtering or sublimation of the material ofthe shell on the insulator, and terminating in an electrode portionextended toward said electrode to establish a spark gap and being cutaway to provide for passage of gases into and out of said sleeve.

ROBERT A. BELL.

